Trichomonas vaginalis (TV) infections are the most common treatable STI worldwide, and among women, are associated with poor reproductive health outcomes and possibly acquisition of HIV. Repeat TV infections are common and better treatment options are needed. This project will examine the influence of index treatment, host factors and partner treatment on repeat TV infections among HIV-negative women in three specific aims: Aim 1: Index treatment- Multi-dose (7 day 500 mg BID - alternative regimen) vs. single dose (2 g - recommended regimen) of MTZ for the treatment of TV. Aim 2: Host factors - To determine if altered vaginal flora, as measured by Nugent score, interferes with TV treatment. Aim 3: Partner treatment - To determine if patient delivered partner treatment is superior to partner referral for reducing repeat TV infections. These aims will be accomplished by conducting a phase IV, two factorial randomized clinical trial among TV infected HIV- negative women (N=2883) attending an STD in New Orleans, LA and an STD clinic in Jackson, MS. These public clinics serve mostly African American, low income women, the demographic group most highly affected by TV. Merging methodologies from our prior RCTs of these two interventions, women will be randomized to a single dose/PDPT, single dose/PR, multi-dose/PDPT or multi-dose/PR arm. Test of cure will be conducted at 1 month. Detailed sexual histories and treatment adherence will be collected weekly via electronic diaries and at one-month via computer-assisted self-administered interviews. Specimens of women who are TV+ at TOC will undergo MTZ susceptibility testing and TV genotyping (to compare baseline and follow-up types). Specimens will be stored for future microbiome studies of the vaginal flora. The information obtained from this study will be used to refine treatment recommendations and examine the translation of PDPT for use in the context of TV. Given the strong multi-centered, RCT design, and the large sample size, results should rapidly inform treatment guidelines thus having high impact. The ultimate goal is improved reproductive health for women, particularly minority women, and the reduction of the potential for HIV transmission, fitting well with NIAID's mission.